Motor control system for electric elevator installations



July 14, 1931.

E. O. ANDERSON MOTOR CONTROL SYSTEM FOR ELECTRIC ELEVATOR INST ALLATIONS Filed May 20. 1927 2 Sheets-Sheet l INVENTOR.

July 14;=1931. E, ANDE S N 1,814,501

MOTOR CONTROL SYSTEM FOR ELECTRIC ELEVATOR INSTALLATIONS Filed May 20. 1927 2 Sheets-Sheet 2 INVENTOR. @fi fi am A T TORNEYS.

Patented July 14, 1931 FATE??? GFFEE EDWIN O. ANDERSON, OF JERSEY CITY, NEW JERSEY 1VIOTOR CONTROL SYS'IEIK FOR ELECTRIC ELEVATOR INSTALLATIONS Application filed May 20,

My invention relates to an improved motor control system, and has for one of its objects the provision of an improved motor control system which is particularly adapted to ele vator installations.

A still lurther object of my invention is the provision of a motor control system which is adapted for automatic control of the motor which drives the elevator car means being arovided so-that by the-simple throwing ot a switch the control may be changed to a car switch or manual control, in that the movement of the car is controlled by the operation of the car switch, as distinguished from manipulation of push buttons at car landings or in the car itself.

A. still further object of my invention is the provision oi motor control system in which when applied toelevators, the car may be called from a landing toany other landing, assuming that no push button in the car has been operated, means being provided whereby upon the pushing 01" a button (closing of a switch) at a 'floor landing the car, regardless of the landing at which it may be standing at that moment, will automatically start up and come to rest at the landing at which th push button was operated, assuming also that no other landing push button or our button was operated.

A still further object of my invention the provision of a motor control system particularly adapted for elevator work, in which the car can be automatically controlled by a passenger riding in the car in much the same manner as thecontrol just referred to in connection with floor landing control. In other words, by themere closure of a push button switch within the car, the car will automatically start in motion and proceed to the floor corresponding to the button operated in the car and will automatically come to rest at that floor.

A still further object of my invention is the pro 'ision of a motor control system adapted for elevators, in which means are provided for preventing reversal of the mo tor, and hence reversal of the car, by the operation of a push button, at a landing which has already been reached and passed by the Serial No. 192,856.

car. For example, it the elevator is descending from the third floor to the first floor, after it has left the third floor it rannot be reversed until it has reached the tirst floor, unless the stop push button in the car is first operated. Likewise, withrespect to the sec ond floor on the same trip, the car cannot be reversed after it has passed that floor by the operation of the button at that floor.

Consequently, assuming a passenger enters the car at the toird' tloor landing and presses the car button for the first floor, the car must proceed to the first floor as long as the car button not again.manipulated, or unless a person standing at the second floor landing o orates the button at that landing before the car has reached that landing.

A still further object of my invention is the provision of a motor control system in which the position of the car in the hatchway in part detern'iines what L ay be done with the car by way of directing its mo ment, floor selectors being provided for "his purpose which operate automatically so as to set the entire syste n for certain predetermined operations.

A still further object of my invention is to provide a motor control system in which when applied to elevator installations all doors and gates, i. e., landing doors and car gates, must be closed before the car can be set in motion, thereby providin the maximum in safety in operation. This is quite essential when installations are made in apartment buildings, where the car is operated throughout a great part of the time by women and children.

A still further object of my invention is the provision of a motor control system in which on the down travel of the elevator car, a person at a lower landing may operate the hall push button at that landing to stop the car at that landing, the car after the passenger has entered the same and closed the hatchway door and car gate, automatically resumin 0' its trip, without the manual manipulation of push buttons or other switches.

In the accompanying drawings Figs. 1 and l together constltute a wiring di am of on HI one embodiment of my invention, no attempt having been made to show the switches and various other parts of the mechanical side of the installation in detail, inasmuch as the same will not be claimed herein. In order, also, that the drawings may be simplified as much as possible, I have shown a three iloor installation, it being understood that the same plan can be extended to as many floors as desired. By showing three landings, however, I am given upper and lower landin s and an intermediate landing, wnich are surl'icient for purposes of explanation and clarity of description.

The installation shown is for alternating current, but, as will be understood from the detailed description, my invention is adapted equally well for direct current work.

I might mention also, before entering into a detailed explanation, that but one motor is necessary for driving the car, as dis tinguished from systems now in operation in which a main and an auxiliary motor are employed.

Referring to the drawings in detail, M desi nates an alternating current motor which is to be controlled by my improved system, and which it is to be understood is adapted to drive an elevator car (not shown) in both directions. T S designates a throwover switch, shown in neutral position, but which when thrown down adapts the motor for push button operation, and when closed in the opposite direction adapts the motor M for car switch ope ation. The car switch is designated C S, the car push buttons, 1 for first floor. 2 for second floor, and 3 for third floor, while the landing or hall buttons are designated 4 at the first floor or landing, 5 for the second floor or landing, G for the third floor or landing. The hatchway door contacts are designated 7, 8 and 9, and the gate contacts, i. e., the contacts closed by the closure of the car gate, are designated 10 and 17.

Assuming the throw-over switch 'l. S to be closed in a down iiosition, and that the hatchway doors, car gate, etc. are all closed, the control system is ready for push button operation or control from any of the floor landings or from the car itself. The car is as sumed to be standing at the first floor.

It will be assumed, of course, that the main line knife switch (not shown) has been closed.

A passenger upon entering the car at the first floor and closing the hatchway door and car gate, I will assume, presses the car push button for the third floor, 3. The operation from then on until the car reaches the third floor, is as follows:

Current flows from phase 11, by way of conductor 12, through safety switch 13, conductor 14, through stop button 15, which is in the car and provided for stopping the car at any time, as distinguished "from an automatic stop, conductor 16, gate contact 17,

conductor 18, through blade 19 of throw-over switch l S, conductor 20, to normally closed contacts 21 on dashpot 64, conductors 92, 149, 22, push button 3, conductor coil 24 of floor relay 25 for the third floor, conductor 26, stud 27, conduct r 28, through normally closed contact 29 on first tloor selective relay 30, conductor 31, blade 32 ot' throw-over switch T S, conductor 33, through top nor mal limit switch 34, conductor 35, through coil 36, on up reversing switch 37, conductor 38, through normally closed insulated interlock contact 39, conductor 40, stud 41, conductor 42, governor switch 43, conductor 44, through top emergency limit switch 45, con ductor 46, through bottom emergency limit switch 47, conductor 48, to phase I.

When current flows through the up revers ing switch coil 36, up reversing switch 37 closes, and at the same time current passes through coil 24 of third floor relay to close the same. .he closure of up reversing switch 3? permits current to How through insulated auxiliary contact 49 on the up reversing switch. At the same time another auxiliary contact, 50, on the up reversing switch is closed. With the auxiliary contacts 49 and 50 closed, current may flow through cam motor 51. Operation of this cam motor 51 will cause the door contact 7 to close, permitting current to flow through coil 52 of potential switch (30 from conductor 18, through gate contact 10, conductors 53 and reverse phase relay contact 55, conductor 56, potential switch coil 52, conductor 5?, closed door contacts 7, 8 and 9, conductor 58, through closed contact 49 on up reversing switch, con ductors 59 and 40, stud 41, conductor 42, governor switch 43, top emergency bottom emergency 47, conductor 48, to phase l. Potential switch 60 will now close.

The closure of potentia switch (30 closes insulated normally open auxiliary contact 61 on the potential switch, permitting current to flow through blade 19 0t throw-over switch T H through comluctor 20, contact 61, conductor ('33, direct floor relay 25. The push button 3 may now be released without opening the circuit of the motor M. As the potential s itch (l0 closes the dashpot ($4 thereon will gradually open contacts 21 to open feed wire 22 to all three car push buttons 1, 2 and and also teed wire to third floor hall push button 6.

So far as first floor and intern'iediate hall buttons are concerned, that is, buttons 4 and 5, the circuit through. these buttons is at this time open due to the tact that on closure of the up switch 37 dashpot (35 thereon will open contacts 66 in series with'these push buttons.

is the car leave" the first floor on its upward travel, cont s (37, which in practice are mounted on floor selector (38, will automatically close, due to a mechanical moion not shown, and when the car passes the second floor, fioor selector contacts 69 close. It will be'obvious thatselectorcontacts are unnecessary for the third floor in the three floor installation assumed herein, but ii in practice, as will be the case, there are more than three floors, selector contacts will be provided at all floors except the upper floor.

Also, as the .car passes the second floor, floor selector contacts 70, previously closed for up motion open and close for down mo tion. This is also a mechanical operation not shown in detail. The purpose of this arrangementis to enable a passenger entering the car at the first floor to press the second floor car push button 2 and to have the car ascend to the second fl0or,-and to stopat that floor. If, however, the third floor car push button has been operated, as we assumed in the first instance, the passageof the car past the second fioor instead of stopping at that floor, would not only cause floor selector contacts-70 to open from up position but to close to down position, thereby placing these contacts in such position that the car, after passing the'second .floor and stopping at the third floor, for instance-could be called to the secondfloor.

I will assume, howeventhat the passenger entered the .car at the first floor, pressed'the third floor car push button, :andascended to the third floor. The car as it reaches the third floor will stop automatically by reason of the fact that it w-illzopen the top normal limit switch 34 mechanically. This mecha nism is not shown, as the same will not be claimed in detail herein.

1 will next assume that a passengerenters the car at the third floor, and operates the rst floor car push button 1, and as the car begins to descend a passenger on the second floor landing operates the .hall button 5 at that floor. Under such conditions the operation will be as follows:

Upon closure of car push button 1, current will flow from phase 11 through the same conductors, switches, gate contacts, knife switches,etc. as already described in connection with the operation of push button 3, up to conductor 22, the current instead of flowing through push button 3, now flowing through push button 1, and from there through conductor 71,-stud 72, conductor 73, branching at 74, through conductor 75, coil 7 6 of first floor selective relay 77, conductor 7 8,.branching at 7 9,conductor 80, iloorselector contact 67, conductor 81, blade 82 of throw-over switch T S,-conduc'tors 83, stud 41, conductor 42, governor switch 43, conductors 44, top emergency limit 45, conductor 46, bottom emergency limit 47, conductor 48, to phase I. The passage of current through .coil 76 of first floor selective relay 77 causes this relay to close and this relay becomes self-holding, inasmuch as current can now pass fromstop button 15, conductor 84, branching at 85, conductor 8.6, branching at 87 conductor 88, conductor .89,contacts 90 of first floor selective relay 30, conductor 91, to branch 74, and from there to phase I through the circuit already traced.

At this timecurrent flows from auxiliary contact 21 on dashpot 64, through conductor 92, branching at 93, conductor 94, through normally closedautomatic start relay 95, con- 1 ductor 96, branching at 97 conductors 98, 99, 100, normally closed contact 101 on second floor selective relay 125, conductors 102, 103, contacts 77 on first floor selective relay 30 conductor 105, contact on first floor relay 106, coil 107 of said relay, conductor 108, to stud 1.09, branch conductor 110, knife switch blade 111, conductor 112, bottom normal limit switch 113, which at this time is closed, conductor 114, coil of the downswitch 116, conductor 117, contacts 113 on dashpot 119, conductor 120, normally closed insulated interlock contact 121, conductor 59, and from there by way of conductors, etc. alrcac'ly traced to phase I.

The coil of down'switch 116 nowibeing eX- cited, the switch will close and dashpot 119 will open contacts 113, while auxiliary contacts 122011 the down switch williclose, thereby maintaining'a circuit through the .coil of ili' the down switch.

YVith'theclosing of the down switch 110, auxiliary contact 123 on the downswitch will close so as to establish a circuit for the cam motor 51,:theother phase of this motor at the same timebeingclosed by reason of auxiliary contact 124 on down reversing switch 116 closing because ofthe closing of the down reversing switch, as already explained. The

operation ofthe cam motor efi'ects closure of door contact 9.. The closure of door-contact 9-establishes a circuit for the coil 52 on potential switch60 and potential switch-closes to complete the motor circuit.

The motor will now start in adown direction and continue running until the reaches first floor, at which time the motor will automatically stop, due to opening 01" bottom limit 113. If, however, a passenger at the second floor should have operated second floor hall button 5 before the car on its down trip reached that .floor, the car instead of "proceeding to the first floor without interruption will automatically come to rest at the second'fioor. Thereason forthis is:

Upon operation of the push button 5, the second floor selective relay 125 will close, a circuit being established for its .coil. 126 by way of :branch :85, conductors 127., 128, 129,

normally closed contacts 66 on dashpot 65,

conductor 130,:coil 13-1 01 master magnet 132, conductor 133,;blade 134of throw-overswitch T S, conductor 135., second :fioor hall push button5, conductor 136, 'colil 126 for the second floorselective relay 125,.conductor 2137,

second floor selector contact 69, which are at this time closed due to the car having on its up trip passed the second floor, conductor 81, and from there to phase I, this circuit having already been traced.

The exciting of the coil 126 causes second floor selective relay 125 to close and at the same time to open its back contacts 101. l/Vhen second floor selective relay closes, current can pass through the coil 138 of the second floor relay 139, and this relay will close to establish another circuit for the coil 115 of the down switch 116. Now, therefore, although the back contacts 101 011 the second floor selective relay have opened so as to interrupt the circuit through these contacts to the coil 115 on the down switch, another circuit has been established for this coil, with the result that the car will continue to run toward the first floor.

As the car reaches the second floor, the fioor selector contact will be opened mechanically, thereby interrupting the circuit to the coil on the down switch 116, and consequently this switch will open, thereby interrupting the circuit to the driving motor M, and the car will come to rest at the second fioor.

The passenger waiting at the second floor may now open the hatchway door and the car gate and enter the car.

Upon the opening of the down switch 116 above referred to, the dashpot 119, which has been prevented prior to the opening of the down switch from closing its contacts 118, will be released and move its contacts toward closed position, the dashpot being so designed as to give the passenger at the second floor suflicient time to open the hatchway door. The opening of this door will open the door contacts 8, which are in series with the coil 52 of the potential switch 60, so that until the door has been closed, the potential switch 60 will remain open. Likewise, the opening of the car gate will open the gate contacts 10 and 17, the opening of these contacts, which are in the circuit of the coil 52 of the potential switch and the circuit of both up and down switch coils 36 and 115, respectively, will prevent the potential switch and the two reversing switches from closing. Accordingly, the car must remain at rest at the second floor landing until both hatchway door and car gate are closed. The dashpot 119 in the meantime, of course, has closed its contacts 118.

WVhen the passenger at the second floor opened the car gate the contact 17 opened and current will flow through the coil of automatic start relay 95, and this relay will close to open contacts carried thereby, and insert resistance 14:2 in the circuit of the coil 115 of down switch 116 to prevent this switch closing. Hence, the down switch 116 must remain open until the gate contacts 17 are again closed. Also, when the gate was opened, contacts 10 were opened, and these contacts being in the circuit for the coil 52 of potential switch 60, this switch cannot close until the gate contacts 10 have been closed. Accordingly, even though the resistance 1412 be accidentally or deliberately short-circuited, no circuit could possibly be made for the motor M, inasmuch as the potential switch 60 would still be open.

Upon closing of the hatchway door and car gate, the contacts 17 and 10 will. be closed. The closure of the gate contacts 17 short-circuits the coil 140, and hence the contacts of the relay 95 will close, short-circuiting the resistance 1 12. Suflicicnt current may then fiow through the coil 115 of the down reversing switch 116 through a circuit previously traced when the first fioor car push button 1 was operated for descent of the car from the third fioor.

The condition now exists that a circuit has been closed through the coil 115 of the down reversing switch; and a circuit through the coil 52 of potential s vitch 60; consequently, with these switches closed the motor circuit will be closed in down direction and the car will automatically start up and proceed to the first fioor, where it will auton1atically come to rest.

It will be seen, therefore, that as so far described, a motor control system for elevators has been. provided, wherein by the manipulation of a car push button with the elevator car at the first floor, the car will automatically proceed to a floor (third floor, for instance,) corresponding to the button which has been operated. It will be seen also that a passenger in the car at the third fioor, for example, may by operation of car push button corresponding to the first floor, for instance, on use the car to autematictlly start up and pro ceed toward the first fioor. It will be seen also that while the car is proceeding toward the first floor a person at an intermedia e floor (the second floor, for example) may by pressing hall button at his floor cause the car to stop automatically at that floor, and after he has entered the car and closed the hatchway door and car gate the car will automatically start in motion again and proceed to the ground floor.

Assuming that the car after stopping at the first floor has been sent to the third fioor again, and while standing at that floor the hall button at the first floor and the hall button at the second floor are operated. The car would, had the second floor button not been operated, have proceeded to the first floor. but by reason of the operation of the second. fioor button, the car will stop at the second floor and thereafter auton'iatically proceed to the first floor. The circuit for our operation upon operation of the second floor push button is identical with the operation above described not 132,-closes .the master magnet, and 0.1--

Ycuit' may be traced from phase 11 through conductor 12,,satety switch 13, uctor 1%, stop button 15, conductors 84,127, 128, 129, contacts 66 on dashpot (35,, these contacts beingnormally closed, contacts up reversing [switch-37, conductor 130, coil 131 on master magnet 132,.conductor 133, knife switch blade 134, on throw-over switch T S,,conductor 135, 1 'rst floor hall push button 4, conductor 118, stud .72, conductor 73, and from there the circuit .is identical with that traced when firs; floor car push button 1 was operated. The COfl'.76.0f tl1e'fiTSt floor relay now being energized,.the relay ,willclose-its two pairs of ,contactsQO and 77.

Energization of the c0il-131 of master in rent may now flow throughthe master magnet,,conductor144t, coil 1&5 of mastermagnet 1&6, conductor 147, stud 11 to conductor 42. 'ilheclosureot thesecond master magnet 1&6

closes contacts 14.8, ,and current can flow through the coil 115 ofdown reversing switch 116 vtoclose the same. The circuit is from branch 9-3,.conductor 14.9, relay contacts 1 18, conductor 150, to conductor98, and from thence.asipreviously traced. The closure of the down reversing switch closes the circuit for the cam motor '51, so that thesame will close the circuit for thepotential switch coil 52, .whereupon.the potential switch .will close its and completeithedown circuit for the mo- .tor iM.

Thepperations above described are pusa button operations. It for any reason it should bedesiredto control the motor by car switch 30 S, it 18 merely necessaryto close tl10SW1tCl1 T s'inoppo'site direction, whereupon operation of .carlever 151 to'the right .willclosea circuit to. the motor M and down revers ng. switch 116, whilemovement of the lever inthe-opposite direction will close the circuit .for up reversing switch 37.

,While 'I have illustrated anddescribed a motor. control system adapted for electric elevator installations whereinthe system isse- .lective on down motion of the elevator car, in that the car canbe stopped on down motion,

at fan intermediatelanding, by operation of a landing-push button, itis to beunderstood that this .hasi-been done forthe purpose of clarity and simplicity ofeXpla-nation and not by way. 011411111152113101'1, inasmuch as, obviously,

the system mayQreadilylbe made selective .on

up motion or in both directions, if desired, within the purview of my invention.

It is to be understood also that where I refor to the operation of a push button switch, this is but a momentary operation, as distinguis ed ram systems of push button control wherein the push button must be held closed.

It will be apparent from the foregoing that l have provided an electric motor control system in whichthe objects set out in the above descriptionare attained in a simple and inexpensive manner, and while I'have referred to certain specific types of control devices, it is to be understood that these devices may be changed both as to construction and their location in the circuits of my improved system, without departing from the spirit and scope of my invention;

I wish it-to be understood and appreciated vator car, car push button switches for controlling the CllCUltOff said motor to effect travel of the car to any desired landin landing push button switches operable independently of the operation of the car push buttons to effect movement of the car to any desired landing, saidYlanding push buttons being inoperative on up motion of the car underthe control of acarpushbutton, and operable on down motion of the car at intermediate landin rs independently of the car push buttons but, dependently ot the position of the car with respect to the desiredintermediate landing, and means for automatical- 1l effecting restarting of the car from an intermediate landing without operation ol',

the car push button.

2. In a motor control system for electric elevator installations, the combination of an electric drivlng motor iior effecting move- .ment of. anelevator car in its hatchway, car

push button switches for controllingthe circuit of said motor, thereby toefliectmovement of the car in either direction oi travel from a landing to another landing landingpush button switches operable when the .car push button switches are in neutral position .to etfectmovement of the car froma landing to any one of a plurality oflandings. said landing push button switches after the operation of a car push button switclibeing operative to interrupt the motor circuitonly in down direction of rotation of themotor and prior to the arrival of the car at the'landing correspondingzto the landing button operated, .and switch mechanism operable automatically to effect a closure of the motor circuit in a down direction a predetermined intcrval after the said interruption of the motor circuit.

8. In a motor control system for electric elevator installations, the combination of an electric driving motor, an intermediate floor selective relay, a landing push button switch adapted upon operation to eilect closure of said relay, back contacts carried by said relay, said contacts opening upon closure of said. relay, a reversing switch in the motor circuit, a coil for said switch the circuit of which is opened due to the opening of said back contacts, a floor relay the circuit of which is closed by the closure of the said intermediate floor selective relay, said floor relay maintaining a circuit through the said reversing switch after the opening of the said back contacts on the intermediate floor selective relay.

4. In a motor control system for electric elevator installations, the combination of an electric driving motor, a car push button switch adapted to control the motor circuit to effect travel or an elevator car from one landing to another landing, an intermediate floor selective relay corresponding to an intermediate landing, a landing switch corresponding to said relay and adapted when closed to effect a closure of said relay, back contacts carried by said relay and moving to open position upon the operation of said landing switch, a reversing switch in the circuit of said motor, a coil for said reversing switch the circuit of which is initially through said back contacts, a floor relay the circuit 01": which is closed by the closure of the said intermediate floor selective relay, the said floor relay maintaining a circuit through the coil of the reversing switch after the opening of the said back contacts.

5. In a motor control system for electric elevator installations, the combination of an electric motor for driving the elevator car, car push button switches for controlling the circuit of said electric motor, an intermediate landing push button switch for stopping the car at an intermediate landing, an automatic start relay, a reversing switch for said motor, back contacts carried by said start relay opened when the relay is closed to insert resistance in the circuit of said reversing switch to prevent automatic closure of the same, car gate contacts adapted when closed to short-circuit said resistance to permit the reversing switch to close, whereby the elevator car after stopping at the intermediate floor landing will be automatically started.

6. In a motor control system for electric elevator installations, the combination of an electric motor for driving the elevator car, relays inthe control circuit of said motor corresponding to the ditferent car landings and adapted to close the main circuit of the motor, a coil for each relay adapted to close the relay and maintain the same in closed position, car push buttons operable to close the circuit of the relay coil corresponding to the button operated thereby to effect travel of the car toward, a predetermined landing, ad ditional relays in the control circuit of said motor, and a landing push button at each landing operable to selectively close said additional relays to interrupt the main circuit of said motor to stop the car at a plurality of intermediate landings corresponding to the landing buttons operated without turther operation of the car push buttons.

7. I11 a motor control system for electric elevator installations, the combination oi an electric driving motor, a main circuit and operating circuits therefor, landing push buttons at landings intermediate the terminals of the installation, relays selectively controlled by said landing buttons, car push buttons operable to selectively control said operating circuits to in turn close the main motor circuit selectively, the operation of any of said intermediate landing buttons, opening, through said relays, the operating circuit previously closed by a car push button switch, and closing another operating circuit for the motor.

8. In a motor control system for electric elevator installations, the combination of an electric driving motor, relays in the operating circuit of said motor corresponding to the different car landings and adapted selectively to close the main circuit of the motor, car push buttons operable selectively to effect operation of said relays, landing push buttons for eiiecting an interruption of an opcrating circuit previously closed by operation of a car push button and the closure of another operating circuit to stop the car at an intermediate landing corresponding to the landing button operated, said landing push buttons being inoperative after the car has passed the floor at which the landing button is operated.

9. In a motor control system for electric elevator installations, the combination of an electric driving motor, car push buttons for controlling the circuit of said motor to effect travel of the car toward a landing corresponding to the car push button operated, landing push buttons for taking the control of the car away from the car push buttons to stop the car at a landing corresponding to the landing button operated, said car buttons being so arranged that operation of one button of the plurality will prevent the others from functioning, and so that it the car is brought to rest at a landing intermediate the starting point and the terminal corresponding to the first car button operated, control of the car is retained by the first car push button operated to stop the car at the landing corresponding to the first car button operated, after the car has been brought to rest at an intermediate landing.

10. In a motor control system for electric elevator installations the combination of an electric driving motor for effecting travel of the elevator car, car push button relays for controlling the operating circuit of the motor to eli ect travel of the elevator car toward landings corresponding to the car push button relays operated, hall or landing push button relays for selectively interrupting the operating circuit of the motor to stop the car on down motion only, at intermediate landings, reversing switches controlled by and adapted to be opened and closed by said car push button relays and said landing push button relays, and car gate contacts for preventing closure of the circuit of either of said reversing switches while the gate contacts are in open position.

EDWIN O. ANDERSON. 

